When the first buses comprising gearboxes were constructed, the engine was mounted in front and the gearbox was positioned beside the driver. The control lever for the gear box was mounted directly in the gearbox and its control was thus easy and direct. A drawback was the fact that the gearbox, and thus the control lever, was directly connected to the engine and moved and rattled along with the engine. When the engine was moved to the centre or ever to the rear of the bus, this method of coupling the gear lever directly to the gearbox could no longer be used. The control problem was solved by mounting the lever in the floor near the driver and connecting it to the gear box via a long rod. The gearbox was still controlled fairly directly, but greater operating forces were required due to the increased number of bearing points. Since the control lever was still directly connected to the gearbox, it still moved along with the gearbox and the engine and still passed noise into the interior. In addition to that the increased operating mass occasionally caused the gearbox to change to neutral of its own accord upon abrupt braking.
When subsequently manufacturers started to build high-deck motor coaches, it often appeared to be impossible to guide the selector rod past the luggage spaces between the two axles of these high-deck coaches. A solution for this problem was found in coupling the gearbox to the control lever via Bowden cables. This made it possible to manoeuvre past all obstacles. Since both the inner and the outer cables are thereby connected to the vibrating motor on the one hand and to the stationary chassis on the other hand, the engine movement is no longer passed to the control lever, so that the latter no longer moves along with the engine and cannot slip out of gear so easily any more. Due to the fact that the outer cables of the Bowden cables are rubber-mounted and the inner cables slightly function as springs, the noises from the engine and the gearbox are no longer transmitted to the control lever, and consequently they are no longer transmitted to the interior, either.
With the present gearboxes the changing of gears is carried out by the control lever in four directions of movement, viz. to the left or to the right for selecting the gear train, and then forward or backward for engaging the gear. With the known control systems the transmission of said movements from the control lever to the gearbox takes place via two Bowden cables. The cables are alternately loaded in tension and compression thereby, and move forward or backward in their outer cables. At the gearbox the movements of the cables imparted by the lever are converted into reciprocating and rotating movements respectively of the selector shaft. Said selector shaft is thereby moved up or down for selecting the gear train and subsequently rotated clockwise or anti-clockwise for changing gears.
As a result of the reversal of the direction of the forces exerted on the inner cables said inner cables will make contact with the outer cables in the inside bends when loaded in tension and in the outside bends when loaded in compression. All this results in a back lash when changing from pull to push. This back lash is furthermore even increased as a result of the fact that the cable is extended in the direction of pulling and shortened in the direction of pushing before movement is actually transmitted. This leads to the movements of the control lever becoming larger and the sense of direct operation being lost.